Since the Yamanote line is a loop line, "inner" and "outer" are the terms used to differentiate between the directions the trains run in. The trains that run clockwise are the "outer loop" trains, while the trains that run counter-clockwise are the "inner loop" trains.
Comments
Since the Yamanote line is a loop line, "inner" and "outer" are the terms used to differentiate between the directions the trains run in. The trains that run clockwise are the "outer loop" trains, while the trains that run counter-clockwise are the "inner loop" trains.
I hope this helps!
Japan Experience
If you imagine the Yamanote loop as two adjacent rings, inner and outer, it becomes apparent which direction the trains would be going.